Multi-ratio transmission

ABSTRACT

A multi step transmission comprising planetary gearsets (P 1 , P 2 , P 3 , P 4 ), shafts and shift elements. The sun gear of gearset (P 1 ) couples drive shaft ( 1 ). The carrier of set (P 1 ) couples shaft ( 3 ), which couples housing (G) via brake ( 03 ), shaft ( 1 ) via clutch ( 13 ) and shaft ( 6 ) via clutch ( 36 ). Shaft ( 6 ) couples the ring and sun gear of gearsets (P 2  P 3 ) respectively, and, via clutch ( 68 ), shaft ( 8 ), which couples the carrier of gearset (P 4 ). Shaft ( 1 ) couples the carrier of gearset (P 4 ). Shaft ( 7 ) couples the ring gear of gearset (P 1 ) and the carrier of set (P 2 ). The sun gear of gearset (P 4 ) couples shaft ( 4 ), which couples housing (G) via brake ( 04 ). The ring gear of gearset (P 3 ) couples shaft ( 5 ), which couples housing (G) via brake ( 05 ). Output shaft ( 2 ) couples the carrier of gearset (P 3 ) and the ring gear of gearset (P 4 ).

This application is a National Stage completion of PCT/EP2010/062130filed Aug. 19, 2010, which claims priority from German patentapplication serial no. 10 2009 028 720.5 filed Aug. 20, 2009.

FIELD OF THE INVENTION

The subject invention relates to a multi step transmission of aplanetary design, in particular an automatic transmission for a motorvehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, andtypically are connected to a start-up element, such as a hydrodynamictorque converter or a fluid coupling, that is subject to a slip effectand is provided optionally with a lock-up clutch.

Such an automatic transmission is known, for example, from theapplicant's DE 199 49 507 A1, according to which two non-shiftablefront-mounted gear sets are provided on the drive shaft and generate tworotational speeds on the output side, which, in addition to therotational speed of the drive shaft, can be selectively meshed with ashiftable double planetary gear set acting on the output shaft byselective engagement of the shift elements such that only one of the twocurrently actuated shift elements must be engaged or disengaged to shiftfrom one gear to the next higher or lower gear.

By using five shift elements, seven forward gears are obtained; by usingsix shift elements, nine or ten forward gears are obtained.

Furthermore, a multi step automatic transmission with eight forwardgears and one reverse gear is known from DE 102 13 820 A1, and itcomprises a first input path T1 of a first transmission ratio; an inputpath T2, which features a larger transmission ratio than this input pathT1; a planetary gear set of the Ravigneaux type with four elements,wherein the four elements are placed as a succession of elements in arotational speed diagram as a first element, a second element, a thirdelement and a fourth element: a clutch C-2, which transfers torque ofthe input path T2 to the first element S3; a clutch C-1, which transferstorque of the input path T2 to the fourth element S2; a clutch C-4,which transfers torque of the input path T1 to the first element; aclutch C-3, which transfers torque of the input path T1 to the secondelement C3; a brake B-1, which produces meshing of the fourth element; abrake B-2, which produces meshing of the second element; and a driveelement, which is coupled with the third element S3.

Furthermore, a nine-speed multi step transmission is known from DE 29 36969 A1; it comprises eight shift elements and four gear sets, whereinone gear set serves as a front-mounted gear set and the main gearingincludes a Simpson set and a further gear set serves as reverse gearing.

Additional multi step transmissions are for example known from theapplicant's DE 102005010210 A1 and DE 102006006637 A1.

Automatically shiftable vehicle transmissions, of the planetary design,are already generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a low number of shift elements, and minimize the need fordouble shifting when sequential shifting is performed, thereby ensuringthat only one shift element is ever switched when shifting is performedin defined groups of gears.

The applicant's document, DE 102008000428.3, which is not yet published,discloses a multi step transmission of a planetary design that includesan input shaft and an output shaft which are disposed in a housing. Theknown transmission includes at least four planetary gear sets which aredesignated, in the following, as the first, second, third, and fourthplanetary gear sets, at least eight rotatable shafts which aredesignated in the following as the drive shaft, output shaft, third,fourth, fifth, sixth, seventh, and eighth shafts, and at least six shiftelements comprising brakes and clutches, whose selected engagementproduces different transmission ratios between the input shaft and theoutput shaft, and therefore preferably nine forward gears and onereverse gear can be realized.

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, form a shiftable front-mounted gear set,wherein the third and fourth planetary gear sets form a main gear set.

In the known multi step transmission, it is provided that the carriersof the first and second planetary gear sets are coupled together via thefourth shaft, which is connected to an element of the main gear set, thering gear of the first planetary gear set is coupled with the sun gearof the second planetary gear set via the eighth shaft, which isdetachably connectable to the drive shaft via the first clutch, and thatthe sun gear of the first planetary gear set can be coupled with atransmission housing by means of the third shaft, via a first brake, andis detachably connectable to the drive shaft via a second clutch, andthe ring gear of the second planetary gear set can be coupled to atransmission housing by means of the fifth shaft, via a second brake. Inaddition, the seventh shaft is constantly connected to at least oneelement of the main gear set, and can be coupled with a transmissionhousing via a third brake, and the sixth shaft is constantly connectedto at least one further element of the main gear set and is detachablyconnectable to the drive shaft, via a third clutch; the output shaft isconstantly connected at least to one further element of the main gearset.

In the known transmission, the fourth shaft is preferably constantlyconnected to the ring gear of the third planetary gear set, the sixthshaft is constantly connected to the ring gear of the fourth planetarygear set and to the carrier of the third planetary gear set, and isdetachably connectable to the drive shaft via the third clutch.Furthermore, the seventh shaft is constantly connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to atransmission housing via the third brake. In this case, the output driveis produced via the output shaft that is constantly connected to thecarrier of the fourth planetary gear set. Furthermore, the third andfourth planetary gear sets can be combined or reduced to a Ravigneauxset with a common carrier and a common ring gear.

SUMMARY OF THE INVENTION

The objective of the present invention is to propose a multi steptransmission of the initially described type, which has nine forwardgears and at least one reverse gear having a sufficient transmissionratio, in which the design complexity and the overall size, inparticular the overall length and the weight, are optimized, and inwhich efficiency is improved with respect to drag losses and gearinglosses. In addition, in the multi step transmission according to theinvention, minimal support moments should act on the shift elements. Thetransmission, according to the invention, should be particularly suitedfor a front transverse installation.

Accordingly, a multi step transmission, according to the invention, of aplanetary design is proposed which has an input shaft and an outputshaft which are disposed in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shafts, and at least six shift elements comprising brakes andclutches, whose selective engagement produces different transmissionratios between the drive shaft and the output shaft, such thatpreferably nine forward gears and one reverse gear can be realized.

The planetary gear sets, viewed axially, are disposed in the sequence offirst planetary gear set, second planetary gear set, third planetarygear set, fourth planetary gear set, and are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier on which the planetary gears arerotatably supported, the planetary gears meshing with the sun gear andthe ring gear. As a result, when the carrier is held in place, the ringgear has a direction of rotation that is opposite that of the sun gear.In contrast, a simple plus planetary gear set comprises a sun gear, aring gear and a carrier, on which inner and outer planet gears arerotatably supported, wherein all inner planet gears mesh with the sungear and all outer planet gears mesh with the ring gear, and each innerplanet gear meshes with only one outer planet gear. As a result, whenthe carrier is held in place, the ring gear has the same direction ofrotation as the sun gear.

According to the preferable embodiment of the invention, the sun gear ofthe first planetary gear set is connected to the drive shaft, whereinthe carrier of the first planetary gear set is connected to the thirdshaft, which can be coupled with the transmission housing via a firstbrake, and is detachably connectable via a second clutch to the sixthshaft, the sixth shaft is connected to the ring gear of the secondplanetary gear set and the sun gear of the third planetary gear set anddetachably connected to the eighth shaft connected to the sun gear ofthe fourth planetary gear set, via a third clutch, and the drive shaftis connected to the carrier of the fourth planetary gear.

In addition, the ring gear of the first planetary gear set is connectedto the seventh shaft, which is connected to the carrier of the secondplanetary gear set, the ring gear of the third planetary gear set iscoupled with a transmission housing via a third brake, the sun gear ofthe second planetary gear set is connected to the fourth shaft, whichcan be coupled with a transmission housing via a second brake, and theoutput shaft is connected to the ring gear of the fourth planetary gearset and the carrier of the third planetary gear set.

Thereby it is provided that the first planetary gear set is blockable bythe engagement of a first clutch, wherein the first clutch is preferablydesigned as clutch, which detachably connects the third shaft to thedrive shaft, or it is designed as clutch, which detachably connects thethird shaft to the seventh shaft.

The embodiment of the multi step transmission, according to theinvention, results in transmission ratios that are particularly suitablefor passenger vehicles, and in a greater overall gear ratio of the multistep transmission, thereby improving driving smoothness andsignificantly reducing fuel consumption.

Furthermore, construction expenditure is significantly reduced with themulti step transmission, according to the invention, due to a smallnumber of shift elements. According to the invention, the multi steptransmission offers the advantage of enabling to perform the start-upwith a hydrodynamic converter, an external start-up clutch, or even withother suitable external start-up elements. It is also conceivable toperform the start-up using a start-up element integrated into thetransmission. Preferably, a shift element that is actuated in the firstforward gear and in the reverse gear is suitable.

Moreover, the multi step transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Furthermore, low moments are present in the shift elements and in theplanetary gear sets of the multi step transmission, therebyadvantageously reducing wear in the multi step transmission. Inaddition, the low moments make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments in terms ofpower flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following examples,supported by the attached figures. They depict:

FIG. 1: a schematic view of a first preferred embodiment of a multi steptransmission according to the invention;

FIG. 2: a schematic view of a second preferred embodiment of a multistep transmission according to the invention;

FIG. 3: an example of a shift schematics for a multi step transmissionper FIG. 1; and

FIG. 4: an example of a shift schematics for a multi step transmissionaccording to FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multi step transmission, according to the invention,which has a drive shaft 1, an output shaft 2, and four planetary gearsets P1, P2, P3 and P4 which are disposed in a housing G. Planetary gearsets P1, P2, P3 and P4, in the example shown in FIG. 1, are designed asminus planetary gear sets. According to the invention, at least oneplanetary gear set can be implemented as a plus planetary gear set ifthe carrier and ring gear connection are exchanged and, simultaneously,the value of the stationary transmission ratio is increased by 1 incomparison to the embodiment as a minus planetary gear set.

In the embodiment shown, the planetary gear sets, viewed axially, aredisposed in the sequence P1, P2, P3 and P4.

As shown in FIG. 1, six shift elements are provided, namely, threebrakes, 03, 04, 05 and three clutches 13, 36, and 68. The spatialdisposition of the shift elements can be arbitrary, and is limited onlyby the dimensions of the outer design. The clutches and the brakes ofthe transmission are preferably implemented as friction shift elementsor lamellar shift elements.

Selective shifting of nine forward gears and one reverse gear can berealized using these shift elements. The multi step transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaft isthe first shaft, and the output shaft is the second shaft of thetransmission.

The multi step transmission, according to the invention, as shown inFIG. 1, provides that the sun gear of the first planetary gear set P1 isconnected to the drive shaft 1, and the carrier of the first planetarygear set P1 is connected to the third shaft 3, which can be coupled witha transmission housing G via a first brake 03, and is detachablyconnectable to the drive shaft 1 via the first clutch 13 and to thesixth shaft 6 via a second clutch 36. Engaging the first clutch 13 makesit possible to block the first planetary gear set P1 by coupling the sungear with the carrier.

As depicted in FIG. 1, the sixth shaft 6 is connected to the ring gearof the second planetary gear set P2 and the sun gear of the thirdplanetary gear set P3, and via the third clutch 68, is detachablyconnectable to the eighth shaft 8, which is connected to the sun gear ofthe fourth planetary gear set P4, wherein the drive shaft 1 is connectedto the carrier of the fourth planetary gear set.

According to the invention, the ring gear of the first planetary gearset P1 is connected to the seventh shaft 7, which is connected to thecarrier of the second planetary gear set P2, the ring gear of the thirdplanetary gear set P3 is connected to the fifth shaft 5, which can becoupled with a transmission housing G via a third brake 05, and the sungear of the second planetary gear set P2 is connected to the fourthshaft 4, which can be coupled with a transmission housing G via thesecond brake 04; the output shaft 2, in the embodiment example shown, isdirectly connected to the carrier of the third planetary gear set P3 andthe ring gear of the fourth planetary gear set P4.

According to the invention, the first clutch 13 and the second clutch36, viewed axially, can be aligned between the first and the secondplanetary gear sets P1, P2, and the third clutch 68, viewed axially, canbe aligned between the third and the fourth planetary gear sets P3, P4.

Furthermore, the second and third brakes 04, 05, viewed axially, arepreferably aligned side-by-side.

The design example shown in FIG. 2 differs from the design example perFIG. 1 by the characteristic, that the first clutch is designed asclutch 37, via which the third shaft 3 is detachably connectable to theseventh shaft 7, so that blocking of the first planetary gear set P1 canbe performed by coupling the carrier of the first planetary gear set P1with the ring gear of the first planetary gear set P1.

FIG. 3 shows an example of a shift pattern of a multi step transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift pattern shows, as examples, the particular transmission ratiosi of the individual gear steps, and, to be determined therefrom, thegear increments or step changes phi to the next higher gear, wherein thevalue 9.002 is the transmission ratio spread.

Typical values for the stationary transmission ratios of the planetarygear sets P1, P2, P3 and P4 engineered as minus planetary gear sets are:−1.953, −2.191, −2.235 and −2.404, respectively. FIG. 3 shows thatdouble shifting or group shifting is avoided when shifting sequentially,since two adjacent gear steps share two shift elements. It is also shownthat a large transmission ratio spread is attained with small gearincrements.

The first forward gear results from the engagement of the second andthird brakes 04, 05 and the second clutch 36; the second forward gearfrom the engagement of the third brake 05 and the first and secondclutches 13, 36; the third forward gear from the engagement of thesecond and third brakes 04, 05 and the first clutch 13; the fourthforward gear from the engagement of the second and third brakes 04, 05and the third clutch 68; the fifth forward gear from the engagement ofthe second brake 04 and first and third clutches 13, 68; the sixthforward gear, preferably designed as the direct gear, from theengagement of all the clutches 13, 36, 68; the seventh forward gear fromthe engagement of the second brake 04 and the second and third clutches36, 68; the eighth forward gear from the engagement of the first brake03 and the second and third clutches 36, 68, and that the ninth forwardgear results from the engagement of the first and second brakes 03, 04and the third clutch 68; wherein the reverse gear results from theengagement of all the brakes 03, 04 and 05.

Since the brakes 04 and 05 are engaged in the first forward gear and inthe reverse gear, these shift elements can be used as start-up elements.

In the instance that according to the design example per FIG. 2, thefirst clutch is designed as clutch 37, via which the third shaft 3 isdetachably connectable to the seventh shaft 7, the fourth gear, incontrast to the shift schematics per FIG. 3, results from the engagementof the third brake and the first and third clutch 37, 68, as is depictedin FIG. 4; in this case the transmission spread amounts to 9.001.

According to the invention, different gear increments can also resultfrom the same gear pattern depending on the shift logic, thereby makingit possible to realize an application-specific or vehicle-specificvariation.

According to the invention, it is possible to provide additionalfreewheels at each suitable location of the multi stepped transmission,for example, between a shaft and the housing, or possibly to connect twoshafts.

According to the invention, an axle differential and/or a distributordifferential can be disposed on the drive side or on the output side.

Within the scope of an advantageous development, the drive shaft 1 canbe separated from a drive motor, as needed, by a clutch element, whereina hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, awet start-up clutch, a magnetic powder clutch, or a centrifugal clutchcan be used as the clutch element. It is also possible to dispose such astart-up element in the power flow direction after the transmissionwherein, in this case, the drive shaft 1 is continuously connected tothe crankshaft of the engine.

The multi step transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the engine andthe transmission.

Within the scope of a further, not represented embodiment of theinvention, a wear-free brake, for instance, a hydraulic or electricretarder or the like, can be disposed on each shaft, preferably on thedrive shaft 1 or the output shaft 2, which is of special significancefor use in commercial vehicles in particular. Furthermore, a powertake-off drive can be provided on each shaft, preferably on the driveshaft 1 or the output shaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes can be used, for instance, lamellar clutches, band brakes, and/orcone clutches.

A further advantage of the multi step transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

Obviously, any structural embodiment, in particular any spatialdisposition of the planetary gear sets and the shift elementsindividually and relative to each other, and insofar as it istechnically expedient, falls under the scope of protection of thepresent claims, without influencing the function of the transmission asspecified in the claims, even if these embodiments are not explicitlyrepresented in the figures or in the description.

REFERENCE CHARACTERS

-   1 first shaft, drive shaft-   2 second shaft, output shaft-   3 third shaft-   4 fourth shaft-   5 fifth shaft-   6 sixth shaft-   7 seventh shaft-   8 eighth shaft-   03 first brake-   04 second brake-   05 third brake-   13 first clutch-   36 second clutch-   37 first clutch-   68 third clutch-   P1 first planetary gear set-   P2 second planetary gear set-   P3 third planetary gear set-   P4 fourth planetary gear set-   i transmission ratio-   phi step change-   G housing

The invention claimed is:
 1. A multi step transmission, of a planetarydesign for an automatic transmission for a motor vehicle, comprising: adrive shaft (1); an output shaft (2); first, second, third and fourthplanetary gear sets (P1, P2, P3, P4) disposed in a transmission housing(G), each of the first, the second, the third, and the fourth planetarygear sets (P1, P2, P3, P4) comprising a sun gear, a carrier and a ringgear; a third rotatable shaft (3), a fourth rotatable shaft (4), a fifthrotatable shaft (5), a sixth rotatable shaft (6), a seventh rotatableshaft (7), and an eighth rotatable shaft (8); at least six shiftelements (03, 04, 05, 13, 36, 37, 68) comprising a first brake (03), asecond brake (04), a third brake (05), a first clutch (13, 37), a secondclutch (36) and a third clutch (68) whose selected engagement producesdifferent transmission ratios between the drive shaft (1) and the outputshaft (2) such that nine forward gears and one reverse gear can beachieved; wherein the sun gear of the first planetary gear set (P1) isconnected to the drive shaft (1); the carrier of the first planetarygear set (P1) is connected to the third shaft (3) which is connectableto the housing (G) via the first brake (03), and the third shaft (3) isconnectable to the sixth shaft (6) via the second clutch (36); the sixthshaft (6) is connected to the ring gear of the second planetary gear set(P2) and the sun gear of the third planetary gear set (P3), and thesixth shaft (6) is connectable, via the third clutch (68), to the eighthshaft (8) which is connected to the sun gear of the fourth planetarygear set (P4); the drive shaft (1) is connected to the carrier of thefourth planetary gear set (P4); the seventh shaft (7) is connected tothe ring gear of the first planetary gear set (P1) and the carrier ofthe second planetary gear set (P2); the sun gear of the second planetarygear set (P2) is connected to the fourth shaft (4), and the fourth shaft(4) is connectable to the housing (G) via the second brake (04); thering gear of the third planetary gear set (P3) is connected to the fifthshaft (5) which is connectable to the housing (G) via the third brake(05); the output shaft (2) is connected to the carrier of the thirdplanetary gear set (P3) and the ring gear of the fourth planetary gearset (P4); and the first planetary gear set (P1) is blockable byengagement of the first clutch (13, 37).
 2. The multi step transmissionaccording to claim 1, wherein the first clutch (13) detachably connectsthe third shaft (3) to the drive shaft (1).
 3. The multi steptransmission according to claim 1, wherein the first clutch (37)detachably connects the third shaft (3) to the seventh shaft (7).
 4. Themulti step transmission according to claim 1, wherein the first, thesecond, the third and the fourth planetary gear sets (P1, P2, P3, P4)are each minus planetary gear sets.
 5. The multi step transmissionaccording to claim 4, wherein a first forward gear is achieved byengagement of the second and the third brakes (04, 05) and the secondclutch (36); a second forward gear is achieved by engagement of thethird brake (05) and the first and the second clutches (13, 36); a thirdforward gear is achieved by engagement of the second and the thirdbrakes (04, 05) and the first clutch (13); a fourth forward gear isachieved by engagement of the second and the third brakes (04, 05) andthe third clutch (68); a fifth forward gear is achieved by engagement ofthe second brake (04) and the first and the third clutches (13, 68); asixth forward gear is achieved by engagement of the first, the second,and the third clutches (13, 36, 68); a seventh forward gear is achievedby engagement of the second brake (04) and the second and the thirdclutches (36, 68); an eighth forward gear is achieved by engagement ofthe first brake (03) and the second and the third clutches (36, 68); aninth forward gear is achieved by engagement of the first and the secondbrakes (03, 04) and the third clutch (68); and the reverse gear isachieved by engagement of the first, the second, and the third brakes(03, 04, 05).
 6. The multi step transmission according to claim 3,wherein a first forward gear is achieved by engagement of the second andthe third brakes (04, 05) and the second clutch (36); a second forwardgear is achieved by engagement of the third brake (05) and the first andthe second clutches (37, 36); a third forward gear is achieved byengagement of the second and the third brakes (04, 05) and the firstclutch (37); a fourth forward gear is achieved by engagement of thethird brake (05) and the first and the third clutches (37, 68) a fifthforward gear is achieved by engagement of the second brake (04) and thefirst and the third clutches (37, 68); a sixth forward gear is achievedby engagement of the first, the second, and the third clutches (37, 36,68); a seventh forward gear is achieved by engagement of the secondbrake (04) and the second and the third clutches (36, 68); an eighthforward gear is achieved by engagement of the first brake (03) and thesecond and the third clutches (36, 68); a ninth forward gear is achievedby engagement of the first and the second brakes (03, 04) and the thirdclutch (68); and the reverse gear is achieved by engagement of thefirst, the second, and the third brakes (03, 04, 05).